The present invention relates to an intake manifold assembly for use with an engine, and more particularly to an intake manifold assembly having a variable intake passage length for use with an automotive engine.
Intake manifolds for engines are generally disposed between the intake ports of a cylinder head and a carburetor or throttle body having a throttle valve for controlling the amount of intake air. The intake manifold has as many branch passages as the number of intake ports to distribute the air into the intake ports. To meet the demand for higher engine power output without increasing engine displacement size, there has recently been proposed an intake manifold system of a variable intake passage length as disclosed in U.S. patent application Ser. No. 647,713, filed Sept. 5, 1984 corresponding to Japanese Patent Application No. 58(1983)-248657, now U.S. Pat. No. 4,669,428. According to that proposed intake manifold system, the effective intake passage length is reduced when the engine rotates at a high speed or operates under a high load. With that intake manifold system, the charging efficiency of the engine is increased over a full engine operation range for improved engine output performance.
More specifically, the previously proposed intake manifold system includes longer intake passages and shorter intake passages extending parallel thereto and having auxiliary throttle valves or bypass valves which will be opened when the engine rotates at a high speed or operates under a high load and closed at low engine speed or load, to thereby selectively connect the longer and shorter intake passages to the intake ports of the engine. At a lower engine speed or a lower engine load, the air is introduced through the longer intake passages into the intake ports. At a higher engine speed or a higher engine load, the bypass valves are open to allow the air to pass through the shorter intake passages into the intake ports. Therefore, when the engine operates at a lower speed or load, the air mixture is fed efficiently and effectively under its inertia developed during travel through the longer intake passages. When the engine operates at a higher speed or load, the air supplied through the shorter intake passages is subjected to a smaller degree of resistance. Thus, the charging efficiency of the engine is increased at higher and lower engine speeds or loads, resulting in improved engine power output.
However, the intake manifold system of the above structure has a relatively complex passage arrangement, and is large in size especially where an intake chamber of a relatively large volume is employed as a surge tank. If the intake manifold system is to be associated with an automotive engine, it has been found difficult to provide sufficient space for installing the intake manifold system in the engine compartment in the automobile.